The present invention relates to a non-aqueous electrolyte secondary battery using a porous material comprising an active material as an electrode material.
Positive and negative electrodes of a non-aqueous electrolyte battery, particularly lithium secondary battery, are produced by mixing a powdered active material, a conductive material and a polymer binder, dissolving the mixture in a solvent to form a coating composition, applying the coating composition on a metal foil, drying the coating composition and forming the coated metal foil into a predetermined shape. The proportion of the active material in this electrode is about 40% by volume. The remainder of the electrode is composed of 20 to 30% by volume of binding material, conductive materials, metal foils or the like and 30 to 40% by volume of pores. Accordingly, an electric capacity per unit volume is limited by those, which do not substantially contribute to the capacity of the electrode, such as binding material, conductive materials, metal foils and the like. The metal foil occupies the major portion of the weight of the electrode and also limits the electric capacity per unit volume.
Furthermore, manufacturing of a coat requires a lot of steps such as mixing and dispersing of binding material, application of a coating composition, drying of the coat, calender press and the like, and it is complicated. On the other hand, the electrode material must satisfy required performances peculiar to the coating composition, such as shape of particles and the like. Also, performances, which are not substantially necessary to the electrode material, are required, resulting in increase of the cost.
In a lot of commercially available products, a pair of positive and negative electrodes has a ribbon-like shape, and is placed in a container after winding and crushed into a flattened shape and then the container is sealed. According to this method, the corner portion has poor packing in case of packing in a rectangular container so that the electric capacity per unit volume is further lowered.
Hence, an object of the present invention is to provide a non-aqueous solvent secondary battery, which can reduce the volume of a dead space in an electrode contained in a container of the constituted battery, thereby to increase an electric capacity per unit volume, by using a porous material comprising substantially only an active material as an electrode material.
The another object of the present invention is to provide a non-aqueous solvent secondary battery, which can sufficiently bring an active material into contact with an electrolyte solution, electrically, and can reduce the amount of a metal foil as a current collecting material and a conductive material or make use of them unnecessary, and can increase an electric capacity per unit weight in comparison with the prior art, by using the porous material as the electrode material, rather a powder material.